The present invention relates to a gas valve, and more particularly to a gas valve having an annular seal surface for opening and closing a flow passage of gas.
Conventionally, to use compressed natural gas (hereafter referred to as CNG) as fuel for an automobile engine, there is a CNG regulator having a constitution as shown in FIG. 4 that decompresses the CNG in a gas cylinder loaded on the automobile into a predetermined pressure, as disclosed in JP-A-2000-249000.
A summary of the CNG regulator shown in FIG. 4 will be described.
There is an intake 2 formed on a body 1. The CNG flows into a chamber 8 through a filter 3, a passage 4, a valve portion 6 of a cut-off valve 5, and a flow-in passage 7. A housing 9 is contained in the chamber 8, and a valve body 10 of a gas valve for pressure control is contained in the housing 9 being capable of rising and falling. Further, there is a port 11 formed in the housing 9.
The valve body 10 is opposed to a seat 12 disposed on an upper portion of the chamber 8 being capable of coming in and out of contact with each other. When the valve body 10 moves downward apart from the seat 12, the high-pressure CNG in the chamber 8 is supplied into a decompression chamber 14 through an annular clearance 13. When the valve body 10 moves upward to contact with the seat 12, the CNG in the chamber 8 is not supplied into the decompression chamber 14.
A cover 15 is fixed on an upper portion of the body 1, and a margin portion 16a of a diaphragm 16 lies between the body 1 and the cover 15. The margin portion 16a is held by the body 1 and the cover 15, and the diaphragm 16 serves as a partition between the decompression chamber 14 and an atmosphere chamber 17. A central portion of the diaphragm 16 is held by a diaphragm holder 18 and a shell 19. A lower portion of the diaphragm holder 18 is connected in a fitting state to an upper edge of the valve body 10. The rising of the diaphragm 16 moves the valve body 10 upward to block up the seat portion 12. The falling of the diaphragm 16 moves the valve body 10 downward to open the seat portion 12.
Between the shell 19 and a regulating screw 20 provided in the cover 15, a pressure control spring 21 is provided to force the diaphragm 16 downward. By a balance between the force of the pressure control spring 21 and the gas pressure of the CNG in the decompression chamber 14, the diaphragm 16 is made to rise and fall, i.e., the valve body 10 is made to open and close, thereby keeping the gas pressure of the CNG in the decompression chamber 14 at a predetermined pressure.
The decompressed CNG in the decompression chamber 14 is supplied from an outlet 22 formed in the body 1 to the automobile engine.
In the CNG regulator having such a constitution as mentioned above, a seal surface 10a of the valve body 10 is formed of a metal surface, which is made merely by processing a metal of which the valve body 10 is made.
In the valves that control the passing and cut-off of the gas containing a large amount of water vapor such as the CNG, if an ambient temperature drops below the dew point after a system such as the regulator or the like has stopped, dew condensation causes water drops to deposit on the seal surface 10a of the valve body 10 as well as on every part.
When there are such water drops depositing, if the seal surface 10a of the valve body 10 has the processed metal surface, the water drops depositing on the seal surface 10a remain on it. When the ambient temperature becomes 0xc2x0 C. or lower later, the depositing water drops freeze on the seal surface 10a, and the seal surface 10a is fixed to the seal 12. In this case, it might not be possible to start operating next time.
It is therefore an object of the invention to provide a gas valve for controlling the passing and cut-off of the gas that prevents the freezing and fixing on a seal surface and that prevents a system from being unable to operate.
To solve such problems, the present invention provides a gas valve including a valve body having an annular seal surface, of which seal surface an axis is disposed to extend in a vertical direction, and of which seal surface a diameter becomes larger toward a lower end thereof, wherein a liquid repellent film is provided on the seal surface of the valve body.
In the present invention, if there is gas that contains water vapor in a gas flow passage of an apparatus in which the valve is provided, when an ambient temperature drops below the dew point while the apparatus is stopped, the vapor is condensed to water drops on the seal surface of the valve body. However, the diameter of the seal surface of the valve body becomes larger downward and the seal surface has the liquid repellent film formed on it. Thus, the water drops on the seal surface made by the condensation flow downward by their own weight and do not remain on the seal surface. Therefore, even if the ambient temperature becomes 0xc2x0 C. or lower later, the water drops do not freeze on the seal surface, and the seal surface and the seat will not be firmly fixed to each other because of the freezing. In this way, it is possible to prevent the valve body from being fixed and from not being able to operate at the time when the apparatus starts operating.
Further, according to the present invention, the liquid repellent film may be formed by being coated with a liquid repellent including a fluoroalkylsilane as a main component.
According to the present invention, a fluoroalkylsilane may be used as the liquid repellent. As this has a very high liquid repellent characteristic, it is highly effective in preventing the water drops from remaining on the seal surface.
Still further, according to the present invention, an annular groove portion may be provided lower than the seal surface of said valve body, and be formed annularly around an entire circumference of the valve body.
With this constitution, the water drops that have flown down from the seal surface, as described above, remain and freeze in the groove portion. Therefore, the water drops freeze in a place where they do not cause trouble for the valve operation, thereby preventing the freezing on the seal surface.
Furthermore, according to the present invention, the groove portion may be provided with a water retention member.
With this structure, the water drops that have flown down from the seal surface are retained in the water retention member provided in the groove portion. Therefore, the water is prevented from flowing into a sliding portion of the valve body positioned under the groove portion and from freezing in the sliding portion. It is thereby possible to prevent the valve body from not being able to operate.